Variable reactor



L. L. DE KRAMOLIN 2,200'263 VARIABLE REAcToR May 14, 1940.

Filed Oct. 19 1934 LOW C06/PEN 7 suppl. Y

J .4 .J @fg-f4- ,menton Leo-n Lazclclsau.: d /frzmozin Bgwffwmfw Patented May 14, 1940 STATES PATENT OFFICE Application October 19, 1934, Serial No. 749,088 In Germany October 23, 1933 6 Claims.

The present invention relates to reactors or saturable core devices, such as inductance coils, transformers or the like having cores of low magnetic permeability.

It is known that the inductance of coils having iron cores may be varied by varying the saturation or preliminary magnetisation of the core. For high frequency inductance coils the core must have alow permeability in order to reduce losses and, for example, comprises a comminuted ferromagnetic material such as is known under the trade-mark Ferrocart.

According to the present invention an apparatus is provided comprising a low permeability core on which is wound an inductive winding the inductance Aof which is varied by varying the preliminary magnetisation of the core, wherein the core is arranged in the gap of a separate external permanent or electromagnet for producing a preliminary magnetisation of the core. This arrangement has particular advantages as it enables a strong magnetising ux. to be employed which is necessary in order to obtain a high saturation in low permeability cores. It is preferable to provide a good magnetic contact between the magnet and the core at the flux entry and exit points.

This invention is particularly applicable to the tuning ci radio sets to different transmitters by Varying the saturation and thus the frequency to which the inductive winding is tuned. This may be effected by varying the direct current through a winding on the magnet by means of a resistance, which may be arranged at a remote point ii remote control is desired. Several such inductances may be arranged to be controlled in series by a common saturating current whereby it is possible to obtain a single knob control of several circuits.

The apparatus according to the invention is not limited, however, to the tuning of radio sets to diiierent transmitters, but can also be used in manual or automatic volume control circuits, for example by causing the output from a rectier to vary the degree of saturation and thus vary the coupling between two circuits, such as the amount of feed-back. .lin this way also the selectivity of the receiver can be adjusted and thus it is possible to obtain automatic variable selectivity.

The reactor described is also applicable to automatic tuning circuits, automatic tone control circuits, multiplex telephony circuits, and magnetic amplifiers, and may also be used as modulating and demodulating devices in substitution for the ordinary valves, and for other purposes.

The invention willnow be described with reference to the accompanying drawing in which Fig. 1 shows a reactor according to this in- 5 vention. L

Fig. 2 shows a diagrammatic circuit diagram of a remote control arrangement embodying such a reactor.

Fig. 3 is a section or a iorm of core suitable for use in a reactor according to this invention.

Fig. 4 is an elevation of the core shown in Fig. 3.

Referring to Fig. 1, the reactor comprises an electromagnet 4| which is energised by the energising winding 3. The magnet 4l is constructed of material of relatively high permeability, such as from iron laminations or solid iron. It zmali7 be made from material known commercially as Permalloy.

Between the pole pieces of the magnet 4i is arranged an inductance 2 wound upon a ferromagnetic core 5 of low magnetic permeability. It is preferable to provide a good magnetic contact between the poles oi the magnet and the core.

By varying the current flowing in the winding 3 the field strength between the poles of the magnet 4I is varied whereby the saturation oi the core 5 may be varied vand thus also the inductance of the coil 2. In this way the reactor provides a simple means of adjusting the inductance of the coil 2 to any desired value with out any moving parts being necessary. The inductance 2 may form part of a high frequency oscillatory circuit of a radio receiver so that by means of the reactor according to this invention it is possible to effect the tuning of the circuit by merely varying the current flowing through the` winding 3. This may be effected from the remote point by simple variation of a potentiometer.

A diagrammatic circuit arrangement for the remote control of a high frequency oscillatory electric circuit is shown in Fig. 2. Inthis figure, 5 is the ferro-magnetic core which carries the oscillatory circuit windings 2a and 2b. 3 is the magnetising winding arranged on the magnet 4l as shown in Fig. 1. The oscillatory circuit is associated with the condenser 6 and is connected with the radio apparatus in known manner. In series with the preliminary magnetisation winding 3, is the current source B, which is shown here as a battery but which in most cases will be replaced by a connection to the mains. Also in series with the circuit is the resistance R for controlling the current flowing through the preliminary magnetisation winding and thus the saturation of the ferro-magnetic core 5. By varying the current intensity, the inductance value of the windings 2a and 2b may be varied to tune the oscillatory c'puit to the frequency of any transmitter that it is desired to receive. In the ligure, Ris shown as a resistance variable in steps, whereby stepnby-step variation of the inductance may be obtained, for example for wave-range switching. If continuous tuning by saturation is to be effected, the resistance R may be a continuously variable resistance. Ii it is desired to effect variation of inductance both continuously and in a step-by-step manner, the resistance R may be variab-le in steps and may have a continuously variable resistance connected in series therewith. Alternatively, the resistance R may be continuously variable between the steps, so that subdivision into several separate wave bands, even with a large tuning range of an apparatus, for instance from 200 to 2000 metres or more, is then dispensed with.

Further oscillatory circuits or back-coupling circuits of the apparatus, not shown here for the salte oi simplicity, may be connected to the terminals X. Z is an additional resistance regulating arrangement. the value of which may be adjusted to balance the initial premagnetising valuesV of the individual cores with reference to one another when several inductances are to be varied simultaneously by a common control resistance. If the pre-magnetising windings of the cores are connected in parallel and not in series, the additional resistance Z should not be arranged in parallel but in series with the pre-magnetising windings.

All tunings eiiected by saturation such as hereinbefore mentioned permit in other respects the use of much higher permeabilities than, for instance, are obtained with materials, such as known under the registered trade-mark Ferrocart77 wherein during operation, the inductance value remains unchanged. This is due to the fact that in the case of the materials the permeability of which remains unchanged, the permeabilities must be so chosen that even at the smallest wave length arising, the damping is not too great, whereas in carrying out the present invention, the permeability is so chosen that in the condition of the maximum preliminary magnetisation, the permeability is a minimum, the damping is kept within the desired normal limits for the smallest wave lengths, while in the case of higher wave lengths at which ay higher permeability does not bring any objectionable increase in damping, this increased permeability can then also be effectively utilized.

For cases in which a high degree of curvature 0l the magnetisation curve is desired in addition to a high degree of variation of the permeability at the working point, that is especially in those cases where a modulation phenomenon is desired. there is a certain drawback with cores, such as Ferrocart cores, which have a high sub-division in the direction of the lines oi force, in that the megnetisation curve presents only slight curvatures. There will now be described a magnetic core which has proved to be particularly suitable in such cases. This core, however, is also suitable in all other applications according to this invention.

Figures 3 and i show diagrammatically such a form of inductance core suitable for use in apparatus according to the invention. In these figures, I I is a body of thick pasteboard or other insulating material, which serves not only as a former for the coil. but also to ensure that the radiofrequency winding on the core is suiciently spaced from the conductive core material, whereby disturbing capacitive couplings through the core material are to a great extent avoided. The coil former I I may be in the form of a framework structure, so that the H. F. turns touch the insuiating material only at a small number ol points, a suicient air spacing for the reduction of capacitive noises being provided elsewhere. Since the iinished core in the form herein described forms a sell supporting whole, the insulating former can therefore be mechanically relieved to a great extent.

On the coil .former there is wound a layer of thin ferromagnetic wire I2, for instance. iron wire or better an alloy suoli as Permalloy, in such a manner that a small air-space is left ben tween the individual turns, which considerably reduces capacitive coupling between the individuel wire turns. The thickness of the wire should not greatly exceed a diameter of 0.03 mm., thinner wires being still better.

Alter a layer of wire has been applied in the manner described, leaving sufficient spacings between the individual wires, this layer is preferably fixed and coated by a lacquer of good insulating qualities and of the lowest possible dielectric constant. Following this is an insulating layer I3, such for instance as paper, which is also fixed. and then again, in the same manner as has just been described, another layer o wire or strip is applied. The wire or strip may possibly be produced electrolytically by deposition 0n a conductive base which is then dissolved away. The complete winding thus constitutes 'the core 5 ci low magnetic permeability. At 2a and 2b are shown diagrammatically the arrangement of the high frequency coil windings.

Owing to the relatively low iron or the like content of the core 5, the permeability of course becomes considerably less than in solid cores or cores normally made of laminations, but this is desirable for high` frequency purposes owing to the consequent reduction in iron losses to tolerable limits. Moreover, suicient saturation can be obtained in this manner with less current.

The preliminary magnetisation is produced by arranging the core in the eld of an additional permanent or electromagnet which carries the winding 3, and by removing the insulating body adjacent the poles of the magnet, provision can be made for good magnetic contact where the flux enters and leaves the core.

The cores described can. be most simply produced` economically in the form of closed circular rings since they can then be made on a simple coil winding machine with an arrange ment wellnknown per se for the arrangement of intermediate paper layers between the turns. It may be desirable to use two such cores for carrying out the various connections hereinbefore described, which may be energised by a common direct eurent winding 3.

The control of oscillatory circuits in accordance with this invention may also be carried out by using, in addition to the reactor according to this invention or in place thereof, a condenser the capacity oi which may be varied by means of an applied bias.

it is furthermore obvious that for inductive operations when using cores of ferro-magnetic material they may also be applied to capacitated operations when using condensers dependent on Voltage. Suitably constructed Seignette salt co-ndensers are particularly suitable for such condensers.

While I have shown and described what I consider the preferred embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made Without departing from the scope of my invention as defined by the appended claims.

I claim:

1. A reactor for high frequency electrical circuits, comprising a high frequency core of subdivided ferro-magnetic material; said core being of a low order of magnetic permeability, a coil on said core associated with the high frequency electrical circuit, and an electromagne-t in the field of which said core is arranged, said magnet being sufliciently powerful to saturate at least approximately the low permeability core.

2. A Variable reactor for high frequency electrical circuits, comprising a high frequency core of subdivided ferro-magnetic material, said core being of a low order of magnetic permeability, a coil on said core associated with the high frequency electrical circuits, an electromagnet in the field of which said core is arranged, said magnet being sufliciently powerful to saturate at least approximately the low permeability core, and means for varying the eld strength of the electromagnet.

3. A reactor for high frequency electrical circuits, comprising a high frequency core of comminuted ferromagnetic material, said core being of a low order of magnetic permeability, a coil on said core associated with the high frequency electrical circuit, and an electromagnet in the field of which said core is arranged, said magnet being sufficiently powerful to saturate at least approximately the low permeability core.

4. A remo-te control circuit for radio receivers having an oscillatory circuit determining the frequency of the received waves, comprising a Variable reactor with a high frequency coreof subldivided ferro-magnetic material, said core being of a low order of magnetic permeability and an electromagnet in the eld of which said core is arranged and which magnet is sufficiently powerful to saturate at least approximately the low permeability core; a coil inductively associated with said high frequency core and arranged in the said` frequency determining oscillatory circuit of the receiver; a second coil inductively associated with said core; and a circuit including remote control means and said second coil.

5. Reactor for electrical circuts, comprising a core of subdivided ferro-magnetic material, said core being of a low order of magnetic permeability, a coil on said core associated with the electrical circuit, and a magnet between the poles of which said core is arranged.

6. Reactor for electrical circuits, comprising a core of subdivided ferro-magnetic material, said core being of a lo-w order of magnetic permeability, a coil on said core associated with the electrical circuit, and a. magnet between the poles of which said core is arranged, the strength of said magnet being sufficient to produce a substantial increase in the reversible permeability of said core.

LEON LADISLAUS DE KRAMOLIN. 

